The Occurrence of Heavy Oil Deposits in the Deep Water Provinces of the Greater Campos Basin, Brazil: What We Have Learned!

M.R. Mello and P.W. Brooks
High Resolution Technologies@Petroleum Ltd
www.hrt.com.br

This study, based on an integrated multidisciplinary approach, suggests that all the giant and supergiant heavy oil deposits discovered up to now, in shallow horizons of the Greater Campos Basin, Brazil (Santos, Campos and Espírito Santo Basins), are associated with biodegradation processes and are mainly composed of mixtures of biodegraded and non biodegraded hydrocarbons.

It is well known that almost 98% of the oil, called heavy oil, found and produced so far, in the greater Campos Basin, is located in shallow Upper Tertiary reservoirs that occur in the top of the drift sequences. This is mainly due to the presence of huge turbidite reservoirs placed in these sequences, the very good seismic visualization of the prospects in these shallow horizons, and the economic constrains regarding deep drilling technology.

Despite the abundance of large extension reservoirs in the Tertiary layers, it is critical to understand that all heavy oil deposits comes from the much deeper lacustrine, pré-salt rift, source rock called the Greater Lagoa Feia sequence. This sequence arose due to a unique tectonic and climatic evolution, which created a huge epicontinental pre-salt saline lake complex formed during the Lower Cretaceous in the Southern realm of the South Atlantic Margin, comprising of more than 400 meters of organic-rich source rocks and extending up to the salt boundaries of the mid South Atlantic chain.

Since biodegradation, considered to be the main process for the formation of heavy oil deposits, in the Greater Campos Basin, as well as in several petroliferous basins around the world, is directly related to the depth and therefore temperature in the reservoirs, it would be logical to focus exploration in deeper targets in all the oil fields, heavy or not, found in the Greater Campos Basin.

In most areas of the Greater Campos Basin, heavy oil reservoirs lay above light oil and condensate deposits. As an example, giant light oil/ gas accumulations could be found just bellow the Marlim, Albacora, Roncador, Jubarte, Golfinho, BSS-69 and any other known giant shallow horizon accumulations of the Greater Campos Basin.

New technologies, such as diamondoids, gas geochemistry, HRGT, Pre-Stack Time Migration (PSTM) and 3D petroleum system modeling applied in oil systems from these areas corroborate the existence of huge light oil and gas reserves, in the deep horizons from the Upper and Lower Cretaceous post and pre-salt sections of the Greater Campos Basin.

In this paper we describe a summary of the petroleum systems of the Great Campos basin suggesting that large volumes of lighter oil can still be found at greater depths in deep reservoirs below the heavy oil deposits.

AAPG Search and Discovery Article #90062©2006 AAPG Hedberg Research Conference, Veracruz, Mexico